A laminated glass as well as a tempered glass is widely used as a so-called safety glass for an automobile window. Such a laminated glass is manufactured by laminating two glass sheets with a plastic intermediate film. A polyvinyl butyral resin (PVB) film is generally used as the plastic intermediate film. The PVB film is an excellent material for a laminated glass intermediate film. However, it is known that its adhesive strength decreases due to moisture. In particular, if the moisture content of the PVB film is higher than a certain value, the laminated glass can be delaminated due to a rapid decrease in adhesive strength. Since the delamination causes a decrease in the transparency of the glass, consideration is given to the process for manufacturing a laminated glass and the atmosphere for storing PVB films so as not to increase the moisture content of PVB films.
However, a laminated glass, rather than a tempered glass, has recently been employed not only for a windshield of an automobile but also for a side window. The edge of a glass sheet in a side window is often exposed to the air because the glass sheet needs to be raised or lowered. With such a use that the edge can be exposed, and the penetration and diffusion of moisture from the exposed edge decreases the adhesive strength of the PVB film during a long-term use.
In order to solve such a problem, the following methods are proposed.
(a) Improving the composition of the intermediate film so that its adhesive strength is not easily decreased by moisture.
(b) Filling the edge portions of a laminated glass with a single sealing agent of modified silicone (e.g. see Publication of Japanese Unexamined Utility Model Application No. 63-56230).
(c) Placing a gasket at the edge portion of a laminated glass and injecting a polymeric monomer in a gap formed.
The method of (a) reduces the decrease in adhesive strength to some degree. However, the adhesive film is mainly composed of PVB as well, so that the decrease in adhesive strength due to moisture cannot be solved completely. The method of (b) is effective for preventing the penetration of moisture. However, the appearance of the edges of the glass sheet is damaged by sealing. Also, the manufacturing cost is increased by adding a sealing agent injecting process. The method of (c) has problems from a viewpoint of appearance and manufacturing cost, similar to those of the method of (b).